[YzMENTALzY]

This will be a guide for anyone who have no clue to install the downloaded PUP files into their console. Please note that however you cannot install older firmwares version, like for example you have a 3.50 console and you want to install 3.42 or 3.41 firmwares files. It can only be done with downgrading which requires you to have a special USB device. Although you cannot downgrade 3.55 console at the moment. (Thanks anon for the tip!)

Anyway, let’s get started with these tutorials. Depending on your situation, you may need to install the PUP from the PS3 recovery menu. To do just that, you need to follow these steps below:

1. Make sure the that your PUP file name is PS3UPDAT.PUP. If not, you have to rename it.
2. Ready? Now put the file at /PS3/UPDATE/ folder on your USB drive. Take note of the path folder.
3. Power down the PS3.
4. Now press and hold the power button, the system will startup and shutdown again.
5. Release the power button, then press & hold power again, you’ll hear one beep followed by two consecutive beeps.
6. Release power then follow the on-screen instructions. You’re now in the recovery menu.
7. Connect the USB device and select “System Update.”
8. Hope for the best.

Credit to Carlos. You can install official, custom and modified firmwares with this method.

[Cop]

Good guide man. But i finded nice video tutorial out from youtube. You guys maybe wanna watch ChrisTechTV's video. That was kinda off-topic but here comes something ontopic:
Nice Tutorial! And thanks for the share!

-Cop